I have my new system which consists of Mate 3, 3x FM80 and 3x VFXR3048E inverters. My VFXR3048E units run as master and two slaves. I am just about to put the whole system on the wall. I have my 36 (3x 12 panel 285W) arrays all ready mounted - 1x 12 panels array per FM80. All FM 80s feed a common 48V bus - 48V 600amp lithium battery supply. My frequency is 50hz, system voltage is going to be set at 220V (same as utility average over 3 last months).

1. In Grid Zero mode, what happens when the grid disconnects (say a utility power cut). Does the system need grid power in order to function? In Grid zero mode does the unit sync to the grid frequency?

2. Again, in grid zero mode, the AC pass through from the utility - does this get switched in and out using the internal transfer switch? If so, do I limit the input utility current to that of the transfer switch (30 amps per inverter). I would do this by using an appropriate breaker value on each VFXR3048E AC input (32 amp class B breakers).

3. In the Mate 3 screens, is the Mate 3 aware I have 3 inverters stacked as one (or does it just treat the three up stack as one inverter)? So if I set the total utility pass through current to be 90 amps, it will divide this by 3 and set each inverter to 30 amps (the max)? Will then each inverter switch over to the utility if needed - in sync = 3x 30amp inverter internal C/O relays together = 90 amps?

4. As my VFXR3048E utility inputs will then be fused at 32 amp per inverter, it would make sense to do the same value on the inverter AC output? Although the inverters limit (while inverting) is around 13 amps at 220V, allowing for fast peaks on AC load (motors starting, etc.) - would this 32 amp (per inverter) output breaker be fine (class B so it acts fast).

Hi Dan, I don't have experience with grid zero operation, but I took a look at the manual for your inverters (this makes me somewhat dangerous ), and here's how I'd answer your questions:

grenadapalace wrote:. In Grid Zero mode, what happens when the grid disconnects (say a utility power cut). Does the system need grid power in order to function? In Grid zero mode does the unit sync to the grid frequency?

This is one the manual doesn't seem to address, but I'd be willing to bet your inverters will drop out of grid zero mode if there's an outage, continue powering your loads as long as battery and PV are adequate, and resume grid zero operation when grid power is restored, syncing to the grid when that happens.

grenadapalace wrote:Again, in grid zero mode, the AC pass through from the utility - does this get switched in and out using the internal transfer switch? If so, do I limit the input utility current to that of the transfer switch (30 amps per inverter). I would do this by using an appropriate breaker value on each VFXR3048E AC input (32 amp class B breakers).

The manual says, "The inverter remains connected to the utility grid in case the grid is needed. If large loads require the use of grid power, no transfer is necessary to support the loads." This sounds like the internal transfer switch does NOT operate during normal grid zero mode. I think you've got breaker sizing right, size the inverter AC input breaker according to each inverter’s AC current rating.

grenadapalace wrote:In the Mate 3 screens, is the Mate 3 aware I have 3 inverters stacked as one (or does it just treat the three up stack as one inverter)? So if I set the total utility pass through current to be 90 amps, it will divide this by 3 and set each inverter to 30 amps (the max)? Will then each inverter switch over to the utility if needed - in sync = 3x 30amp inverter internal C/O relays together = 90 amps?

I don't see/understand where you set total pass-through current in the Mate3... You do set each individual inverter’s AC current limit (ports 01, 02, 03), which should sum to the total max input current. For your example you'd set each inverter at 30A AC limit. The manual says "If multiple parallel inverters are installed with an AC source of limited amperage, the total combined amperage settings for all units must be less than the AC input circuit. The Configuration Wizard in the MATE3 can perform this calculation. However, the inverters do not perform this calculation. If the Configuration Wizard or similar tools are not used, divide the input size by the number of inverters and assign an equal part of the amperage to each port." Which (I think) means if your AC source is only capable of 60A then each inverter AC limit would be set at 60÷3=20A AC.

grenadapalace wrote:4. As my VFXR3048E utility inputs will then be fused at 32 amp per inverter, it would make sense to do the same value on the inverter AC output? Although the inverters limit (while inverting) is around 13 amps at 220V, allowing for fast peaks on AC load (motors starting, etc.) - would this 32 amp (per inverter) output breaker be fine (class B so it acts fast).

I'd say yes. Remember in grid zero the grid will augment your inverter's 13A inverting capability so the full 30A AC will be available to your loads.

As I said at the beginning, I haven't any experience with grid zero. Hopefully someone who does can verify or debunk my advice! Good luck!

Cheers for all your advice, and now I understand that the inverters (all 3 acting as 1) will deliver me up to a maximum of 90 amps pass through (say its night and the batteries are worn down to the max DOD setting). The manual says you cant this limit this AC in current within the software, but just by using the appropriate breakers on the AC in.

Like you, I would imagine that, during AC loss, the inverters would generate their own 50hz frequency and output, but then I am thinking how would the inverters re-connect to grid on its return (as the C/O relays are not used) - how to quickly sync the internal inverter 50hz time base to that of the utility. This would have to be mighty fast.

Got it... Looks like I will need to plan a change for my system to use the Mini Grid setting. This doesn't look like it has the single inverter limitation...

With MiniGrid, would either of you know...

1. Do the inverters use their internal transfer switch? If so, when the inverters are stacked, do these get stacked too? (so I can switch more than 30A)2. Does the utility need to be live - i.e. what happens in a utility power cut3. If I read correctly, when I am on utility power in MiniGrid mode, all of my PV will go to the batteries, once these batteries reach a charged level, the inverters will then run - disconnecting the utility and then the PV can charge the batteries and run the system? (My PV is around 10.5KW and my average daily load is around 1.5kw per hour).

Hey Dan, take a look at pages 9 and 10 of the app note Sandra provided. I think it answers your questions, except about stacking. It says you can have multiple Radians but not sure how they are allowed to be configured. - Mike